The overall focus of the proposed research is to gain an understanding of the mechanisms involved in the formation of segregated groups of functionally related to investigate this issue using the lamination of the dorsal lateral geniculate nucleus (dLGN) in the ferret as a model. Our investigation will address three main questions. First, what is the role of the cell surface in the laminar segregation of DLGN cells in normal animals? Our previous data show that there are not more synapses or growth cones in the interlaminar spaces than in layers as laminar segregation begins, suggesting that another mechanism besides directed neuropil growth may plan a role in laminar segregation. We will use neural cell adhesin molecule (NCAM) immunocytochemistry, lectin binding of surface glycoproteins, and 35S-labeling of proteins produced during specific times during development to study the role of the cell surface during the segregation of dLGN cell layers. Second, what is the role of glia during the formation of cell and afferent layers in the dLGN in normal animals? There is considerable evidence that glia play an important role in neural development. We will study their role in the lamination of the dLGN by identification of glia at light and electron microscopic levels using an antibody to glial fibrillary acidic protein (GFAP), serial reconstruction of glial processes, quantification of the changing proportions of neurons to glia during development, and correlation of those changes with the timing of major events in the development of dLGN cytoarchitecture and connections, and determination of the effect on dLGN laminar development of reduction of the glial population using 5-azacytidine. Third, what are the cellular interrelationships and afferent specificities following a failure of laminar segregation? We know that absence of retinal input rsults in a failure of segregation of cell layers. We will study the changes in the cell surface and in the glial population as well as the changes in specificity of the colliculogeniculate projection in the absence of laminar segregation. Insight into the developmental mechanisms we are investigating in the proposed research will help us appreciate which phases of the neural developmental process are most susceptible to environmental perturbations as well as the role of congenital defects such as glial cell abnormalities in deficits in organization of the central nervous system.